1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a gate oxide layer in a semiconductor device.
2. Description of the Related Art
As high integration, high speed, low voltage and low power consumption of a semiconductor device, a gate oxide thickness grows thinner. The gate oxide is generally formed of a silicon oxide(SiO2) having dielectric constant of about 3.85 using thermal oxidation process. However, in this case, as the gate oxide thickness becomes thin, direct tunneling effect is occurred, thereby increasing leakage current.
For solving this problem, one method of forming a gate oxide layer using a stacked layer of a silicon oxide layer and a silicon nitride layer(Si3N4) is suggested. However, since the dielectric constant of the silicon nitride layer is about 7.0, it is difficult to obtain effective gate oxide thickness of 40 xc3x85 or less having high reliability and low leakage current.
Therefore, another method of forming a gate oxide layer using a stacked layer of a bottom oxide layer, a tantalum oxide (Ta2O5) layer having dielectric constant of about 25 higher than the silicon nitride layer and a top oxide layer, is suggested. In detail, a silicon oxide layer as the bottom oxide layer is formed to the thickness of 5 to 20 xc3x85 by thermal oxidation, the tantalum oxide layer is formed to the thickness of 30 to 100 xc3x85 thereon, a TEOS layer as the top oxide layer is formed to the thickness of 10 to 20 xc3x85, and thermal-treating is performed under O2 atmosphere. In this case, physical gate oxide thickness is 45 to 140 xc3x85, while effective gate oxide thickness is 40 xc3x85 or less due to high dielectric constant of the tantalum oxide layer.
However, in case the bottom oxide layer is formed to thin film as described above, its uniformity and reliability are deteriorated. As a result, the barrier property against leakage current and resistance against oxidation of the tantalum oxide layer formed thereon, are deteriorated.
It is therefore an object of the present invention to provide a method of forming a gate oxide layer in a semiconductor device which can obtain low leakage current and high reliability with obtaining effective gate oxide thickness of 40 xc3x85 or less, for solving the problems in the conventional art.
To accomplish this above object, according to the present invention, a NO-oxynitride layer as a bottom oxide layer is formed on a semiconductor substrate and a tantalum oxide layer as a medium oxide layer is then formed thereon. Next, the oxide layer is formed on the tantalum oxide layer. Thereafter, the substrate is thermal-treated under N2O gas atmosphere.
In this embodiment, the NO-oxynitride layer is formed to the thickness of 5 to 20 xc3x85 under NO gas atmosphere by a rapid thermal process or a furnace process. Preferably, the rapid thermal process or furnace process is performed at the temperature of 800 to 850xc2x0 C. with raising or lowering pressure and the flow rate of the NO gas is 5 to 20 l/min.
Furthermore, the tantalum oxide layer is formed to the thickness of 30 to 150 xc3x85 by LPCVD or MOCVD. The top oxide layer is formed to the thickness of 10 to 20 xc3x85 using a TEOS layer or a HTO layer.
Moreover, the thermal-treating is performed at the temperature of 800 to 850xc2x0 C. with raising and lowering pressure by a rapid thermal process or furnace process and the flow rate of the N2O gas is 5 to 20 l/min.
Additional object, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.